Tailoring energy band gap and microwave absorbing features of graphite-like carbon nitride (g-C3N4)

•Tuning optical and microwave absorbing performance of the g-C3N4 by tailoring its morphology.•Fabricating g-C3N4 aerogel based on a novel sintering method.•Modifying morphology and establishing defect onto the g-C3N4 nanostructures using citric acid as a novel precursor.•Using sonochemistry, hydrothermal, and combustion methods as innovative complementary processes to modify the morphology.•Employing polyacrylonitrile as a novel absorbing medium and investigating filler ratio on the microwave characteristics. [Display omitted] Currently, two-dimensional (2D) nanostructures have attracted considerable attentions originated from their salient features. Accordingly, the widespread methods have been used to improve their abilities. In this study, g-C3N4 2D structure was synthesized using a conventional route and its structure was distorted by inserting and exhausting citric acid as a novel defecting precursor by sonochemistry, hydrothermal, and combustion methods as an innovative complementary process. Noteworthy, g-C3N4 aerogel (GA) was obtained by tuning the loading mass fraction of melamine to volume of the alumina crucible. The architected materials were characterized using diffuse reflection spectroscopy (DRS), field emission scanning electron microscopy (FE-SEM), X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), and vector network analyzer (VNA). Furthermore, the surface characteristics of the tailored structures were evaluated by N2 adsorption-desorption isotherms. The analyses attested that the pure crystal and chemical structures of g-C3N4 have been produced while the presented route has enhanced crystallinity and developed defects into the nanosheets. The crystal distortions of 2D structures led to the remarkable optical and microwave absorbing features. Besides, polyacrylonitrile (PAN) was applied as an absorbing medium to prepare microwave absorbers. Interestingly, GA brought a significant reflection loss (RL) of 74.92 dB at 11.85 GHz, whereas defected g-C3N4/PAN 30% illustrated broadband efficient bandwidth as wide as 3.56 GHz with a RL>20 dB.